Interpretive Summary: The H5N1 avian influenza virus infected various poultry species and people in Hong Kong during 1997. To determine the risk of this virus for causing disease in different domestic and wild birds and some mammals, experimental studies were conducted. The AI virus grew in chickens and land-based poultry causing severe disease and affecting most internal organs. Likewise, the virus grew in geese emus, house finches, and budgerigars but they usually only developed nervous system disease. By contrast, the AI virus grew in ducks, house sparrows, and gulls, but did not produce disease. Pigeons, starlings, rats, and rabbits were resistant to infection by the virus. The H5N1 Hong Kong AI has the greatest risk to cause disease in domestic poultry.

Technical Abstract:
Seventeen avian species and two mammalian species were intranasally inoculated with the zoonotic A/chicken/Hong Kong/220/97 (chicken/HK) (H5N1) avian influenza (AI) virus in order to ascertain a relative range of susceptible hosts and the pathobiology of the resultant disease. A direct association was demonstrated between viral replication and the severity of disease, with four general gradations being observed among these species. These gradations included widespread dissemination with rapid and high mortality, neurological disease relative to viral neurotropism, asymptomatic infection or only mild transient depression associated with minor viral replication, and absence of disease relative to minimal to no viral replication. This investigation not only demonstrates that the chicken/HK virus can infect multiple avian species, but also that the virulence of the chicken/HK virus can vary significantly among avian species, including those species which are members of the same order.